In this book, Brian Michael Jenkins draws on 40 years of research on terrorism, most of it conducted at the RAND Corporation. He has played numerous leadership roles at RAND over those years and is today my senior advisor. But his most enduring contributions have been the fruits of his research efforts.

In Brian’s early days at RAND in the 1960s, he focused on the insurgencies in Vietnam and Cambodia, on Vietnamese military institutions, and on the styles and techniques of conflict.

In the late 1960s, Brian began drawing parallels between the rise of urbanization in the war in Vietnam...

Secret Service agents gunned down the first team of assassins before they got to the President, but it was a close call. A second team of gunmen managed to get into the House of Representatives, where they wounded five congressmen. A terrorist bomb caused damage but no casualties at the Senate. Troops took up positions at the Capitol and the White House, both of which had been set ablaze. By sundown, Washington was sliding out of control; columns of black smoke could be seen for miles. Authorities were unable to save the White House, which was completely destroyed by fire....

In mid-2006, nearly five years after 9/11, how is America doing in the global war on terror? The question itself reflects the typically American desire to keep score, to measure progress. Fighting in World War II provided visible mileposts—the invasion of North Africa, the march through Italy, the return to the Philippines, the landing at Normandy, the liberation of Paris, the fall of Berlin, VE Day, VJ Day. It was a bloodier contest, but one in which we knew where we were going.

The Cold War that followed lasted decades, and the current contest could easily do the same....

Action films rarely inquire into the mindsets or motives of villains. The villains are simply presented as bad guys, foils for superheroes. Cyclops is always a monster. Dragons breathe fire. Witches are wicked. One need not ask why.

We are likewise inclined to see terrorists as fiends, wild-eyed expressions of evil, diabolical but two-dimensional, somehow alien—in a word, inhuman. Government officials routinely denounce terrorists as mindless fanatics, savage barbarians, or, more recently, “evildoers”—words that dismiss any intellectual content. The angry rhetoric may resonate with apprehensive homeland audiences, but it impedes efforts to understand the enemy. We cannot formulate...

American actions after September 11, 2001, were a response to a catastrophic attack without precedent in the annals of terrorism. Immediate action was required to prevent further attacks. There was no time for lengthy planning. Action and strategy evolved concurrently, which is not unusual in war. It was no different in World War II, when well into the fighting, the allies were still formulating their grand strategy.

America’s strategy in response to 9/11 was initially sketched out in a series of speeches by President Bush and was later elaborated in a number of official documents. On September 20, 2001, the...

Are we safer now? Since 9/11, it has, not surprisingly, become Americans’ most frequently asked question. On that date, the United States suffered its most violent day since the major battles of the Civil War, worse than Pearl Harbor, worse than D-Day, 18 times worse than the terrorist bombing in Oklahoma City. Americans had little experience with violence on this scale. Security became our paramount concern.

But securing the homeland requires more than proliferating bollards and barriers. It requires strengthening ourselves, and that requires acceptance that the world has changed. Wide oceans no longer provide protection. Distance means little today....